The salt marsh and its root layer

Between the dump and the bay our plan is to interpose a salt marsh. The topmost layer, the root layer, is to function as a septic tank. Aerobic and anaerobic phases alternate with each pulse of the tide. Aerobic respiration and sulfate reduction dominate the activity.

Rhizosphere, living machine, septic tank

  • The root system of cordgrass is maintained in a seasonally varying biomass by the carbon cycle of the salt marsh. It is fractoid (approximately fractal) part of the upper layer of the salt marsh, comprising up to 50% of the volume, and about 50% of the biomass. It extends a few millimeters outward from each root surface, and appears red from ferric oxide accumulation due to oxygen diffusion down the stems and rhizomes of cordgrass. Thus oxidized and reduced regions are closely packed in the root layer. (Pomeroy, 1981, p. 18)
  • We assume (provisionally) that the cordgrass biomass and rhizosphere are unaffected by the leachates.
  • The biomass of cordgrass, and the carbon cycle, may be modeled by the complex dynamical model, MRSH1V6, of the Sapelo Island marsh (Pomeroy, 1981, Ch. 9) or some similar model, or from data taken from a salt marsh closer to Pelham Bay.
  • The fate of a COC in a single pulse of leachate is a decrease in concentration due to diffusion-reaction mediated by microbial reactants.
  • For one of the COCs, ammonium, the bacterial agents will be those of the nitrogen cycle.
  • This diffusion-reaction system, for a single tidal pulse, is the goal of our model. For these geobiochemical reactions, we assume Monod dynamics with a compartment of unknown bacteria.
  • In sum, we regard the upper (root) layer of the cordgrass marsh as a living machine, or geobiochemical reactor, for the bioremediation of COCs pulsing our of the dump, and we simulate their removal individually, that is, one COC at a time.

Revised by Ralph Abraham 16 August 1998